When metal components are welded with the use of a welding beam, automated movement devices are frequently used, which, in order to create the desired welding seam, provide the appropriate relative movement between the components which are to be welded and the welding beam. In order to produce the energy densities necessary to create a “key hole” when welding in deep welding mode, the welding beam is, as a rule, very sharply focussed, such that an extremely high positioning precision must be demanded in relation to the automated movement devices in order for a consistent welding seam quality to be provided. In general, as a rule, degrees of positioning precision for the welding beam are required of less than +/−0.15 mm perpendicular to the run of the welding seam, wherein the welding seam is designed as a butt weld or fillet weld. CNC-controlled Cartesian gantry systems fulfil the requirements for positioning precision, but require high investment costs. Multi-axis robots, which in principle are more economical than Cartesian gantry systems, have, because of natural oscillations brought about by the reorientation of their drive units and the softness of the drives, a minimum positioning repetition precision of +/−0.15 mm at particular axial positions. The precision required with dynamic positioning of the welding beam therefore cannot be achieved with multi-axis robots.
Laser beam welding heads are known from the prior art which have additional means for identifying the welding seam position and for correcting the laser welding head. For example, the principle is known from the German published application DE 103 35 501 A1 of determining the actual true path of the laser welding beam head in an advance run window ahead of the welding beam position, comparing it with previously stored reference data, and carrying out a corresponding correction of the position of the welding beam by taking into account the advance run. The problem with this laser beam welding head is that, because of the complex advance run calculation, high welding speeds lead to path deviations.
The International Patent Application WO 2005/095043 A1 discloses a laser beam welding head with means for determining the reference location of the welding seam position, which by means of a triangulation process determine the profile of the reference location of the welding seam close to the current welding position (“key hole”) and continuously position the laser welding head relative to the determined position of the reference location of the welding seam. Due to the advance run being taken into account between the welding position and the measured position, for the determination of the position of the reference location of the welding seam, with this laser beam welding head, too, the effort in calculating the correction signal for the laser welding beam head is relatively high, such that only insufficient welding speeds are achieved with suitable precision, in particular in the case of the processing of radii in paths.